Apparatus and method for preventing optical fiber and gel from ejecting out of buffer tubes in fiber optic cables

ABSTRACT

An apparatus for connecting buffer tubes including a first block, a second block, and a fastener for assembling said first and second blocks. The blocks contain a pair of tube grooves and a cavity and a and a hole leading into the cavity. A sealant is then inserted into the cavities and allowed to cure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromU.S. Provisional Application No. 61/369,897, filed Aug. 2, 2010 in theUnited States Patent and Trademark Office, the disclosure of which isincorporated herein in its entirety by reference.

BACKGROUND

1. Field

The invention is related to an apparatus and method for preventing thefilling compound (gel) optical fiber from ejecting, flowing orprotruding out of buffer tubes in fiber optic cables.

2. Related Art

Many utilities, city municipals and telephone companies deploy systemsthat use fiber optic cable. Many fiber optic cables contain buffer tubesthat are manufactured with a filling compound (gel). The purpose of thegel is to protect the fibers and act as a water blocking agent toprevent water from tracking into the buffer tubes and damaging thefibers and or fiber performance. Three of the typical types of cablesused are: OPGW: Optical Ground Wire uses both plastic and or stainlesssteel buffer tubes (Aerial applications); ADSS: All Dielectric SelfSupporting cable containing plastic buffer tubes (Aerial applications);and Loose Tube: Multiple cable designs containing plastic buffer tubes(Non-aerial applications).

Buffer tubes contain a filling compound that allows the fibers to floatwithin the tube. The gel also helps allow the buffer tubes to store an,excess fiber length or “EFL.” EFL is the term used when talking aboutthe length of the fiber within the buffer tube compared to the actuallength of the buffer tube. The excess length of fiber within the tubehelps determine the point at which the fiber will see strain. The fiberoptic cables are typically installed and terminated within a spliceenclosure. The splice enclosure is used to help protect the exposedfibers and buffer tubes from all types of elements. An AFLTelecommunications “SB01” splice enclosure is a good example of anenclosure that is used in an aerial application.

After the fiber optic cable has been secured within the spliceenclosure, the buffer tubes are routed within the enclosure and thefibers are then terminated (spliced) within a fiber optic splice tray.

Fiber optic cable may be deployed in several harsh or non-standardenvironments world wide. Two such environments are Extreme Heat andVertical Installations. In rare applications, optical fiber may migrateor flow out the ends of the buffer tubes. The issue is not typical butcan occur due to the viscosity of the filling compound (gel), amount offibers within the buffer tube versus the inner diameter, verticalinstallation length and extreme or sustained temperatures while in avertical position. If a fiber optic product shows signs of migration,the gel and fiber will begin to push its way into the splice enclosureand tray. The end result for this action can be the loss of EFL,bending, kinking or breaking of optical fibers and a possible overallfailure to the optical system.

Due to the abundance of fiber optic cable being installed world wide forcommunications needs, it has become extremely important to maintain andprotect the functionally of our fiber optic networks. For this reason,it is vitally important to have a product and procedure in place thatwill prevent the filling compound and optical fibers from migrating outof the buffer tubes.

SUMMARY

Exemplary implementations of the present invention address at least theabove problems and/or disadvantages and other disadvantages notdescribed above. Also, the present invention is not required to overcomethe disadvantages described above, and an exemplary implementation ofthe present invention may not overcome any of the problems listed above.

A first embodiment of the invention is an apparatus for connectingbuffer tubes including a first bock, a second block, and a fastener forassembling the first and second blocks. The first block includes a pairof tube grooves, a cavity and a hole leading into the cavity. The secondblock includes a pair of tube grooves, and a cavity.

In the apparatus, the second block may also include a hole leading intothe cavity.

In the apparatus the second block may be identical to the first block.

In the apparatus the first and second blocks may each include fourfastener holes.

In the apparatus two of the fastener holes on each of the first andsecond blocks may be threaded.

Another embodiment of the invention is a method of connecting buffertubes that includes cutting a buffer tube into two sections, separatingthe buffer tube sections, placing the buffer tube sections into a pairof grooves on a first block, placing a second block on top of the firstblock, wherein the buffer tube sections are placed into a pair ofgrooves on the second block, fastening the first and second blockstogether, filling a sealant through a hole in said first block into acavity formed between the first and second blocks and allowing thesealant to cure.

The method may also include cleaning the buffer tube sections and afiber in the buffer tube prior to placing the buffer tube sections intothe pair of grooves in the first block.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an embodiment of a block.

FIG. 2 is a plan view of an embodiment of a block.

FIG. 3 is a cross-section view of an embodiment of a block.

FIG. 4 is a perspective view an embodiment of two assembled blocks.

FIGS. 5 and 6 are a plan view and a perspective view an embodimentshowing buffer tubes in a block.

FIG. 7 is a flow chart of an embodiment of a method of the invention.

FIG. 8 is a graph showing test results of an embodiment of theinvention.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the methods, apparatuses and/orsystems described herein. Various changes, modifications, andequivalents of the systems, apparatuses and/or methods described hereinwill suggest themselves to those of ordinary skill in the art.Descriptions of well-known functions and structures are omitted toenhance clarity and conciseness.

Hereinafter, the exemplary embodiments will be described with referenceto accompanying drawings.

The invention is a mechanical solution to prevent filling compound (gel)and optical fibers from migrating out of buffer tubes found in fiberoptic cable designs. It is a clever way of solving potential issuescaused by the flow of gel and optical fibers within a splice enclosure.

The method can also be used as a retro-fit solution for an existingsplice location that has exhibited the migrating issues. The method canpotentially be applied without re-routing or re-splicing the opticalfibers.

FIGS. 1-5 show an embodiment of the invention that can be used on afiber optic buffer tube. Note that while the description describes theinvention being used with fiber optic cables, the invention is notlimited to fiber optic cable and also be used with wired cables. Theapparatus consists of two blocks 1A and 1B. In a preferred embodiment,the block is made of aluminum; however, it could be made of othermaterials, such as plastic, steel, ceramic, glass, rubber, etc. Inaddition, in this embodiment, blocks 1A and 1B are identical, which canreduce manufacture costs. However, the blocks do not have to beidentical. In this particular embodiment, the blocks are 30 mm long by12.7 mm wide by 4.8 mm deep; however, the block is not limited to thesedimensions. The block includes four fastener holes, 4, 5. In thisembodiment, holes 4 are threaded, and holes 5 are not threaded. Thisallows a fastener 12, such as an M3 8 mm screw, to be inserted into hole5 and then screwed into hole 4 when the blocks are assembled. However,all of the holes could be smooth and the blocks could be assembled bynuts and bolts. In addition, other known fastening methods could be usedsuch as hinging one side of the blocks and fastening the other sides ofthe blocks.

The block also includes a filling/exit hole 3 and a cavity 7. When theblocks are assembled, a sealant can be inserted into one filling/exithole and can exit the other filling/exit hole 3 after the cavity 7 hasbeen filled.

The cavity in this particular embodiment is approximately 18 mm long by7.5 mm wide by 1.3 mm deep; however, the cavity is not limited to thesedimensions.

The block also has two tube grooves 6 into which buffer tubes areinserted. The diameter of the grooves 6 are slightly smaller that thediameter of the buffer tubes to ensure a tight fit.

Next, a method a assembling the block on a buffer tube cable will beexplained. See also FIG. 6.

Depending on the type of enclosure selected, a decision should be madein determining the distance needed from the enclosure to for ring cutlocations. The blocks should be applied at a distance long enough awayfrom the enclosure to prevent long term kinking or damage to the opticalunits within the enclosure. In step 1, the buffer tube 10 should be ringcut.

In step 2, the buffer tubes 10 should then be pulled apart approximately20 mm to reveal the fibers. Note that the fibers in the buffer tubes arenot cut.

In step 3 any waterblock gel is removed from the fibers using a standardsolvent spray cleaner and cloth. Ensure that the buffer tubes are cleanand all fibers are clean and intact. Ensure that the fibers have driedbefore proceeding to the next step. Note that the invention may workwithout the buffer tubes and fibers being cleaned; however, long termperformance may be comprised due to the lack of adherence between thecured sealant and un-cleaned fibers.

In step 4, ensuring that each end of the tube is clean and dry, offer upthe first block 1A to tubes 10. The ends of the tube should be flushwith the edge of the cavity 7, and the fibers 11 should be straight asshown in FIG. 5. Alternatively, the buffer tube can be flush with anedge 6A of the groove.

In step 5, position the second block 1B over the tubes, ensuring thatthe filling hole is at the opposite end to the first block 1A. Push theblocks together to trap the buffer tube in place, ensuring the opticalfibers are not trapped between the meeting surfaces.

In step 6, fasten the blocks together. In this particular embodiment, ateach corner of the block insert screws through the plane side of eachhole and use an M3 hexagonal key to tighten.

In step 7, the cavity 7 is filled with a sealant, such as a 10:1 ratio2-part silicone sealant with MSDS silicone sealant. A gun applicator canbe used to fill the cavity 7. Prior to filling, a piece of cloth can bepressed against one of the filling/exit holes 3, blocking that hole. Theapplicator is then placed in the other filling/exit hole 3 and thecavity 7 is filled with the sealant. There should be a pressure build upat the blocked filling/exit holes and when the cloth is removed, theexcess sealant should flow out of the hole. This excess sealant can bewiped away using the cloth. Then lightly pull on the fibers located nextto the entrance of the tray to release any possible movement of thefibers that may have occurred during the sealant injection. The sealantis then allowed to cure.

Once the sealant cures, future tube/fiber migration should be prevented.

This solution was also tested to see how it would affect the performanceof the fibers. The test includes, temperature soaking the migrationrepair at extreme temperatures of −40° C. and 85° C. and aged by cyclingbetween 37° C. and 49° C. The blocks 1A and 1B were assembled and filledwith 2-part silicone sealant as per the methods described above.

The results of the temperature cycling are shown in FIG. 7. Theretro-fit solution was applied to each end of four buffer tubes foundwithin the OPGW cable. Six fibers from each tube were concatenated bymeans of fusion splices to form an optical loop. The total fiber lengthunder test was approximately 700 m. The cable was temperature cycled asfollows:

Soak @ −40° C. for 24 h

Soak @ 85° C. for 24 h

Cycled between 37° C. and 49° C. for 1 week (3 h per cycles)

Soak @ −40° C. for 24 h

Soak @ 85° C. for 24 h.

The change in attenuation per splice was less than 0.05 dB/km andtherefore, the retro-fit solution as tested met the requirements of thetest both optically and visually, no fiber migration was observed.

The solution is to be used at splice enclosures where potential fibermigration is expected or observed. If the fiber migration is alreadypresent, the application may be applied without breaking the existingfibers.

As mentioned above, although the exemplary embodiments described aboveare directed to fiber optic cables, this is merely exemplary and thegeneral inventive concept should not be limited thereto, and could beused with wired cables (e.g., coaxial cables) and corresponding wiredcable interface components and equipment.

1. An apparatus for connecting buffer tubes comprising: a first bock; a second block; and a fastener for assembling said first and second blocks; wherein said first block comprises: a pair of tube grooves; a cavity; and and a hole leading into said cavity; wherein said second block comprises: a pair of tube grooves; and a cavity.
 2. The apparatus of claim 1 wherein said second block further comprises a hole leading into said cavity.
 3. The apparatus of claim 2 wherein said second block is identical to said first block.
 4. The apparatus of claim 1 wherein said first and second blocks each comprise four fastener holes.
 5. The apparatus of claim 4 wherein two of said fastener holes on each of said first and second blocks are threaded.
 6. A method of connecting buffer tubes comprising: cutting a buffer tube into two sections; separating said buffer tube sections; placing said buffer tube sections into a pair of grooves on a first block; placing a second block on top of said first block, wherein said buffer tube sections are placed into a pair of grooves on said second block; fastening said first and second blocks together; filling a sealant through a hole in said first block into a cavity formed between said first and second blocks and allowing said sealant to cure.
 7. The method of claim 6, further comprising cleaning said buffer tube sections and a fiber in said buffer tube prior to placing said buffer tube sections into said pair of grooves in said first block. 